Hydrocarbons, sterols and alkenones in sinking particles in the Indian Ocean sector of the Southern Ocean

Hydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month sediment trap time series deployed in the Indian Ocean sector of the Southern Ocean. Fluxes and within-class distributions varied seasonally. During higher mass and organic carbon (OC) flux periods, which occurred in austral summer and fall, fresh marine inputs were predominant. Vertical fluxes were most intense in January, but limited to one week in duration. They were, however, low compared with other oceanic regions. In contrast, low mass and OC flux periods were characterized by a strong unresolved complex mixture (UCM) in the hydrocarbon fraction and a high proportion of stanols as a result of zooplanktonic grazing. Terrigenous inputs were not detectable. The alkenone compositions were consistent with previous data on suspended particles from Antarctic waters. However, U37K′ values diverged from the linear and exponential fits established by Sikes, E. L. and Volkman, J. K. Calibration of alkenone unsaturation ratios (U37K′) for paleotemperature estimation in cold polar waters. Geochimica et Cosmochimica Acta, 1993, 57, 1883–1889], in the low temperature range. The seasonal pattern of alkenone production implied that IPT (integrated production temperature) is likely to be strongly imprinted by austral summer and fall SST (sea surface temperature).